Vehicles may include a variety of movable closure members including, for example, side windows, rear lift gate windows, power sliding doors, sunroofs, and moon roofs. Utilization of these movable closure members in the normal course of operation of a vehicle can create pinch points adjacent a closed position. It is known in the industry that reducing a speed of travel or movement of movable closure members adjacent the closed position can minimize the effects of such pinch points in the event there is an obstruction during a closing procedure. In fact, vehicle safety standards regulate the amount of force that can be applied to obstructing objects in such scenarios.
One method of controlling the speed of movable closure members common within the industry utilizes pulse width modulation. Pulse width modulation speed control works by driving the motor with a series of “ON-OFF” pulses and varying the duty cycle, i.e., the fraction of time that the output voltage is “ON” compared to when it is “OFF,” of the pulses while keeping the frequency constant. The power applied to drive the motor is controlled by varying the width of these applied pulses and thereby varying the average DC voltage applied to the motor terminals. By changing or modulating the timing of these pulses the speed of the motor can be controlled, i.e., the longer the pulse is “ON,” the faster the motor will rotate and likewise, the shorter the pulse is “ON” the slower the motor will rotate.
One significant drawback to the utilization of pulse width modulation is the creation of electromagnetic compatibility issues. In other words, use of pulse width modulation to control drive motors within the vehicle can create unintentional electromagnetic energy which can cause unwanted effects such as electromagnetic interference or even physical damage in other equipment in the vicinity of the motor. Even more, utilization of pulse width modulation can cause mechanical vibration in certain instances due to the start/stop of the motor. Accordingly, a need exists for a method and related circuits for controlling the speed of movable closure members without creating unwanted electromagnetic interference or electromagnetic compatibility issues. Such a system would move the movable closure members between initial and final positions while allowing for a speed of movement to be adjusted. The adjustments could be designed to overcome retarding forces of seals associated with the movable closure member or to comply with vehicle safety standards at pinch points adjacent a closed position. Ideally, the system would allow the vehicle to operate in full compliance with the relevant vehicle safety standards and would minimize, if not eliminate, any electromagnetic compatibility issues.
In addition, the control circuits could utilize one or more shunts to control motor speed. The shunts could be formed as traces on a printed circuit board having varying resistances. Utilization of traces reduces the space required on the printed circuit board, the number of components utilized, overall cost, the number of component failures, and the overall complexity of the printed circuit board and the overall system by reducing the amount of control software required to provide varying motor speeds. Even more, the utilization of shunts eliminates the need for pulse width modulation control.